The present invention relates generally to a high-speed erasing apparatus for use in helical scanning type magnetic recoding/reproducing systems such as a video tape recorder (VTR).
A helical-scanning type VTR is generally arranged to include a rotational cylinder, having at its circumferential portions a plurality of magnetic heads, around which a magentic tape is wound or wrapped obliquely so as to perform recording or reproducing bf information on and from the magnetic tape by the magnetic heads in accordance with traveling of the magnetic tape concurrently with rotation of the rotational cylinder. Furthermore, known is a depth-recording type Hi-Fi VTR having on its rotational cylinder an audio head and a video head which are disposed to be close to each other. The depth-recording type Hi-Fi VTR is arranged such that an audio signal is recorded at a depth of a magnetic layer of the tape by the audio head and a video signal is further recorded (overwritten) over the recorded audio signal by the video head, whereby as shown in FIG. 5 the video signal and the audio signal are recorded successively along an oblique track T formed by the audio and video heads on the helically guided magnetic tape T.sub.P with a video signal segment of every field. In addition to the audio head 3 and the video head 2, the aforementioned VTR is provided with an audio signal recording fixed head which in turn records an audio signal on a side edge portion of the magnetic tape T.sub.P with it slidably contacting the traveling magentic tape T.sub.P so as to form an audio track T.sub.A. Also included generally in the aforementioned VTR is a full-erasing head 1 for a full-tape width erasure of the magnetic tape T.sub.P which is adapted to erase the previously magnetic signals, before performing recording of a new signal on the magnetic tape T.sub.P.
However, there is a problem which arises with such a VRT in that, because the full-width-erasing head 1 is disposed stationarily to take a preceding position to the video head 2 and the audio head 3 mounted on the rotational cylinder with respect to the tape travel direction, in the cases where the erasing operation is started upon determination of the erasing position determined from a reproduced picture image, a non-erased portion (shadowed portion in FIG. 5) is developed unintentionally between the position of a track recorded with the signal of the reproduced picture image and the full-erasing head 1, thereby resulting in the problem of incomplete erasure of the signal.
One conceivable solution for elimination of the presence of the non-erased portion left on the magentic tape T.sub.P is to set a recording condition without supplying the video signal and audio signal but with erasing signals to the video head 2 and the audio head 3 and let both heads carry on an erasing operation without using full erasing head. In this instance, it takes a longer time, i.e., the same time as normal signal recording operation, thus it would be unable to perform a high-speed erasing operation.
In addition, such a VTR is generally so arranged that the frequency of the erasing current to be supplied to the full-erasing head 1 is about five times (about 70 KHz) the upper limit of the audible frequency range. In this case another problem arises in that upon reproduction of the tape, the frequency of the erasing current is derived in the audible range as disturbing noises.